The present invention relates to an electrically heated aerosol generating system for receiving an aerosol-forming substrate, and a method for electrically heating an aerosol-forming substrate. The present invention finds particular application as an electrically heated smoking system.
A number of prior art documents, for example U.S. Pat. No. 5,060,671, U.S. Pat. No. 5,388,594, U.S. Pat. No. 5,505,214, U.S. Pat. No. 5,591,368, WO-A-2004/043175, EP-A-0 358 002, EP-A-0 295 122, EP-A-1 618 803, EP-A-1 736 065 and WO-A-2007/131449, disclose electrically operated smoking systems, having a number of advantages. One advantage is that they significantly reduce sidestream smoke, while permitting the smoker to selectively suspend and reinitiate smoking.
U.S. Pat. No. 5,388,594, the entire contents of which are incorporated herein by this reference thereto, describes an electrical smoking system. The smoking system includes a cigarette and a reusable lighter. The cigarette is adapted to be inserted in and removed from an orifice at a front end of the lighter. The lighter includes a housing and has a front portion and a rear portion. A power source for supplying energy to heating elements for heating the cigarette is disposed in the rear portion of the lighter. The power source is sized to provide sufficient power for the heating elements that heat the cigarette. The power source is preferably replaceable and rechargeable and, in one preferred embodiment, is a battery. The front portion preferably houses heating elements and circuitry in electrical communication with the power source. The smoking system is used in much the same fashion as a conventional cigarette.
WO-A-2004/043175 also describes an electrical smoking system. In that document, the electrically heated cigarette smoking device includes an upper heater case cap, a front housing and left and right battery case portions. A heater unit is positioned below the heater case cap, with the heater unit fitting inside a partition, which positions the heater unit relative to the front housing of the device. An opening at the top of the heater case cap allows for the insertion of a cigarette into the top opening of the heater unit. When the cigarette has been inserted through the heater case cap opening and into the heater unit opening, it is positioned in proximity to a plurality of heater blades, arranged around the circumference of the cigarette. Slots through the heater case cap provide passageways for ambient air to enter the device when a cigarette is positioned in the opening. A printed circuit board is positioned between the partition and the front housing. A heater unit connector is positioned below the heater unit within inner housing members. This provides electrical connection between the heater blades and a power source such as a battery, housed within the battery case portions.
U.S. Pat. No. 5,060,671, the entire contents of which are incorporated herein by this reference thereto, describes a flavor-generating device with a disposable part constituted by the heater and the flavor-generating medium, and a reusable part constituted by the power source.
Other prior art documents, such as EP-A-0 295 122, EP-A-1 618 803 and EP-A-1 736 065, disclose electrical smoking systems which use a liquid as the aerosol-forming substrate. The liquid may be contained in a cartridge which is receivable in a housing. A power supply, such as a battery, is provided, connected to a heater to heat the liquid substrate during a puff, to form the aerosol which is provided to the smoker.
The electrically heated aerosol generating systems of the prior art, including those described above, typically provide a high power pulse to the heater to provide a high temperature and to release the volatile compounds for each puff.
The electrically heated aerosol generating systems of the prior art, including those described above, do have a number of advantages, but there is still room for improvement in the design. It would be advantageous if the devices could be made smaller, so that the size is closer to that of a conventional cigarette and more convenient for the user.